This invention relates to the cogeneration of electricity and refrigeration by the low NO.sub.x combustion of natural gas or like fuel gas rich in methane and other gaseous hydrocarbons. More particularly, the combustion of fuel gas with low NO.sub.x emission makes it feasible to recover carbon dioxide (CO.sub.2) as a product of cogeneration.
Cogeneration systems have received considerable attention in recent years. Many processes have been proposed for the cogeneration of electricity and saleable refrigeration or heating steam. Many cogeneration schemes are based on the use of gas turbines which have certain disadvantages. For example, U.S. Pat. No. 4,528,811 to Stahl shows several cogeneration systems involving the combustion of fuel gas and passage of the hot combustion products through a gas turbine. Stahl points out that gas turbines are normally operated with about 300% excess air over the stoichiometric requirement. Any large amount of excess air naturally decreases the thermal efficiency of the system. Moreover, in light of the rapidly growing concern about atmospheric pollution by combustion processes, a further disadvantage is being recognized in that the gaseous effluents of gas turbines contain high amounts of nitrogen oxides (NO.sub.x), usually in excess of 100 parts per million (ppm), as well as carbon monoxide (CO) and unburned hydrocarbons.
Accordingly, a principal object of this invention is to avoid the use of gas turbines in congeneration systems by substituting therefor steam turbines.
A related principal object is to generate steam for the steam turbines by introducing fuel gas admixed with air into a porous fiber burner and effecting flameless combustion on the outer surface of the burner to minimize NO.sub.x formation.
A further object is to limit the amount of excess air used in the combustion of fuel gas to yield a flue gas of increased CO.sub.2 content.
Another important object is to recover CO.sub.2 from the flue gas and to utilize the cogenerated refrigeration to liquefy the CO.sub.2.
These and other features and advantages of the invention will be evident from the description which follows.